In general, a suspension is a device for supporting a chassis of a vehicle, and is also referred to as a suspension system.
One type of a suspension comprises mainly a shock absorber, a spring, and a suspension arm, and main functions thereof are to prevent road shocks from being directly transferred to the chassis or passengers by absorbing the shocks and to securely bring tires into contact with the ground.
Therefore, the suspension has a great influence on passengers' riding comfort and drivability and stability of the vehicle.
Suspensions are classified into various types depending on the structure thereof. The most common suspension is a strut-type suspension. As other examples, there are a double-wishbone-type suspension and a multi-link-type suspension.
The suspension is typically configured to absorb shocks using a metal plate and a shock absorber. An ‘electronically controlled suspension’, in which shock absorbing characteristics of a shock absorber are electronically controlled, has been developed, and an ‘electronically controlled air suspension’, which uses an air instead of a metal plate, is also being used.
Further, there has been developed an ‘active suspension’, which employs a hydraulic system having excellent responsibility instead of a plate and a shock absorber and which controls vibration of the chassis appropriately for the traveling states of the vehicle using a computer, thereby ensuring traveling stability and drivability.
Suspensions may be classified into those suitable for a front wheel and those suitable for a rear wheel depending on the mounting position. Generally, a strut-type suspension is mounted to a front wheel, and a rigid axle suspension or an independent rear suspension (IRS) is mounted to a rear wheel.
One end portion of an upper arm is pivotably supported by the chassis and the opposite end portion thereof is pivotably supported by the upper portion of the wheel via an upper ball joint. One end portion of a lower arm is pivotably supported by the chassis and the opposite end portion thereof is pivotably supported by the lower portion of the wheel via a lower ball joint. A shock absorber and a coil spring are mounted between the bottom surface of the chassis and the top surface of the lower arm, and an upper seat plate and a lower seat plate are, respectively, mounted to the upper contact end and the lower contact end of the coil spring at the exterior of the shock absorber.
At this time, the upper and lower seat plates perform pivot motion about the respective center points thereof so as to adjust angles thereof, thereby making it possible to shift the force acting axis of the coil spring to the left or right from the center of the coil spring.
In the suspension system having the above-described configuration, when the force acting axis of the coil spring is shifted, the distance between the wheel and the load contact point of the coil spring varies, thereby making it possible to adjust a wheel rate and a height of the vehicle and consequently to change the riding comfort of the vehicle.
Here, the wheel rate is a suspension spring constant measured at the position of the wheel of the vehicle, and is also referred to as a suspension rate. The wheel rate is indicated by the weight that is required to make the center of the upper end of the coil spring and the center of the wheel come a unit distance (mm) closer to each other, excluding compression of the tire, attributable to a certain amount of load applied thereto.
Further, the coil spring constant measured at the position of the wheel including the tire is referred to as a ‘ride rate’.
A conventional method for adjusting the wheel rate and the height of the vehicle by varying the force acting axis of the coil spring in the aforementioned suspension system is disclosed in Japanese Patent Registration No. 4369418 (Sep. 4, 2009) (Title: Wheel Suspension).
The wheel suspension disclosed in the Japanese Patent Registration No. 4369418 is configured such that, separately from a shock absorber detachably mounted between the bottom surface of the chassis and the top surface of a lower arm, a coil spring is mounted in another space formed between the bottom surface of an upper arm and the top surface of the lower arm, and such that a center line L and a force acting axis W of the coil spring are geometrically changed via rotation, thereby changing the rigidity of the coil spring.
However, in this configuration, because the coil spring is rotatably mounted between the bottom surface of the upper arm and the top surface of the lower arm separately from the shock absorber, the required installation space is unnecessarily increased. In addition, when the coil spring is rotated by a motor, the upper contact end and the lower contact end of the coil spring may be worn, and a coating layer formed thereon may be peeled off by friction. In addition, a portion of the coil spring that is worn or from which a coating layer has been peeled off may be corroded, and the spring may be fractured in severe cases.